Thermosetting resins such as fiber-reinforced plastics (FRPs) have been widely used as a material for bathroom component products such as a bathtub. Unlike thermoplastic resins, thermosetting resins cannot be recycled by melting and remolding them. In addition, the resins generally contain about 70% of inorganic materials such as an inorganic filler, and therefore, the self-combustion of the resins is difficult. Accordingly, most of waste plastics such as FRPs based on thermosetting resins have been dumped by reclaiming lands with the same, since they are very difficult for recycling. However, this waste disposal by way of reclaiming the lands has difficulties in the ensuring of sites to be reclaimed and in stable hardening of such sites. To solve these problems, the Containers and Packaging Recycling Law was instituted in 1995 in Japan, so as to obligate the recovering and recycling of plastics. This trend of recovering and recycling products containing plastics is prevailing in association with the enforcement of a variety of recycling laws.
Under these situations, recently, trials to recycle waste plastics for use as a resource have been attempted. As one of such trials, there is proposed a method of recovering useful oily substances from waste plastics by decomposing the waste plastics through a reaction using supercritical water as a reaction medium. There is also proposed a method of recycling fiber reinforced plastics used in various structural materials, in which the plastic components in such materials are decomposed by using supercritical water or subcritical water, so as to recover fibers such as glass fibers and carbon fibers for recycling them.
By these methods, plastics are decomposed into oily components having lower molecular weights so as to recycle these components as liquid fuels. There is further proposed a method of decomposing plastics, which makes use of a hydrolysis reaction by high temperature water vapor. According to this method, it is possible to decompose the organic polymer components of thermoplastic and thermosetting plastics to some extents.
However, the above methods have a disadvantage in that, since plastics are decomposed in random, the decomposition products are oily materials comprising various components, and thus in that it is difficult to obtain decomposition products with constant qualities. Consequently, a post-treatment for reforming the oily materials by using a catalyst, typically, zeolite, is needed, which results in higher cost. Further, it is difficult to produce petroleum products such as lamp oil and light oil from such reformed oils, and therefore, such reformed oils have not yet been put into practical use.
In the method described in the following Patent Literature 1, the decomposed resin is recycled as an unsaturated polyester resin again. However, the method has problems that the re-cured product of the decomposed resin has different properties from those of the original thermosetting resin (i.e., the resin has lower properties as a thermosetting resin), and the occupancy rate of the decomposed resin in the re-cured product is limited to a low extent, since the thermal decomposition of the decomposed resins is occurred due to the high decomposition temperature.
Recently, there is proposed a method for decomposing a thermosetting resin with subcritical water having a strong hydrolysis ability. More specifically, the method comprises hydrolyzing a thermosetting resin with subcritical water as a reaction solvents recovering the resultant low to middle molecular weight compound, and reusing the compound as a raw material for a resin (see, for example, the Patent Literature 2 and the like).                Patent Literature 1: JP-A-9-221565 (1997)        Patent Literature 2: JP-A-10-024274 (1998)        